The Ordovician system in the United States :
correlation chart and explanatory notes /
by Reuben J. Ross Jr. ... [et al.].

APA Citation

Ross, R. J., International Union of Geological Sciences. International Subcommission on Ordovician Stratigraphy. (1982). The Ordovician system in the United States: correlation chart and explanatory notes. Paris, France: Available from IUGS Secretariat.

MLA Citation

Ross, Reuben J, and International Union of Geological Sciences. International Subcommission on Ordovician Stratigraphy. The Ordovician System In the United States: Correlation Chart And Explanatory Notes. Paris, France: Available from IUGS Secretariat, 1982.